1. Field of the Invention
The present invention relates to a process for producing .alpha.-hydroxyisobutyric acid amide by a hydration reaction of acetonecyanohydrin. .alpha.-Hydroxyisobutyric acid amide is a useful intermediate for production of methacrylamide and methyl methacrylate.
2. Description of Related Arts
A hydration reaction of acetonecyanohydrin in which .alpha.-hydroxyisobutyric acid amide is synthesized in the presence of a sulfuric acid catalyst, and then converted into methacrylamide and methyl methacrylate is well known, as described in, for example, Kirk Othmer "Encyclopedia of Chemical Technology", 3rd Ed., Vol. 15, p. 357. This process is widely carried out on a commercial scale.
The conventional process, however, has disadvantages in that large amounts of waste sulfuric acid and acidic ammonium sulfate are by-produced and the treatment thereof increases production costs of methyl methacrylate.
In order to solve the above disadvantages, various hydration reactions of acetonecyanohydrin using a solid catalyst in place of sulfuric acid have been proposed. As catalysts for the hydration reaction, Japanese Patent Application Laid-Open No. 4068/1972, for example, discloses that a manganese dioxide catalyst is effective, and Japanese Patent Application Laid-Open Nos. 222/1977, 57534/1988 and 57535/1988 disclose that a catalyst containing manganese dioxide as a main component (hereinafter referred to as a "manganese catalyst") is effective.
It is described that, in accordance with these methods, .alpha.-hydroxyisobutyric acid amide can be obtained in a yield of 60% to 95% by carrying out a hydration reaction of acetonecyanohydrin at 40.degree. C. to 100.degree. C. in the presence of a manganese catalyst, preferably in the presence of an acetone solvent, according to the following equation. ##STR1##
In fact, however, it has been found that in the hydration reaction using the above known manganese catalysts, the yield of .alpha.-hydroxyisobutyric acid amide is unsatisfactorily low for industrial use, the catalytic activity is lowered with a lapse of time, although it is high at the initial stage, leading to a rapid decrease in the yield of .alpha.-hydroxyisobutyric acid amide, and thus a stable operation on a commercial scale cannot be expected.
A tubular reactor was packed with a known manganese catalyst, and a feed solution prepared by adding water and a solvent to a distilled reagent acetonecyanohydrin was continuously introduced into the tubular reactor to conduct a reaction. By an analysis of the product solution from the outlet, changes with a lapse of time in the reaction results and the catalyst activity were measured. In the case of the known catalysts, the yield of .alpha.-hydroxyisobutyric acid amide at the initial stage of the reaction was relatively high, but this catalyst activity was rapidly decreased with a lapse of time, leading to unsatisfactory results for commercial use.